Effect of Metformin on Visual Function in Patients With Glaucoma

Inclusion Criteria: * Age between 18-65 years old; * The baseline value of intraocular pressure ≤ 21 mmHg in either eye whether untreated or treated by ≤ 2 eye drops (laser or filtering surgery should be performed over 3 months). * Over two times of experience of visual field examination (24-2 or 30-2 visual field examinations) in the past two years, or false positive/false negative ratio less than 33%; * Diagnosed POAG by Glaucoma specialists from Zhongshan Ophthalmic Center with open angle, and impairment in optic disc or visual field in one or both eyes. * Patient is at risk of glaucomatous progression, as determined by the documented presence of optic disc hemorrhage within 12 months in either eye, OR ≥2 of the following risk factors: * Vertical cup-to-disc ratio \>0.8 in one or both eyes * Mean deviation in visual field worse than \<10 dB in either eye (verified by the reading center) * Pseudoexfoliation in either eye * Family history (parent or sibling) of glaucoma * Hypertension * Systemic hypertension requiring medical treatment Migraine (defined by the International Headache Society with or without aura, Raynaud's syndrome, or both: * The main organs are functioning normally and meet the following criteria: 1. Blood sample should meet the following criteria: (no blood transfusion within 14 days) A. Hemoglobin (\> 90g/L); B. Platelet count (\>105\*10e9/L) 2. Biochemical and urinary examinations should meet the following criteria: <!-- --> 1. . Urine bilirubin \< 1.25 times ULN (Upper Limit of Normal); 2. . ALT and AST \< 2.5 times ULN; 3. . CREA ≤ ULN; Exclusion criteria: * Secondary open-angle glaucoma (such as pigmentation syndrome, trauma, etc.) or angle-closure glaucoma. * The best corrected visual acuity of either eye is less than 6/36; * The mean derivation of visual field in either eye is less than - 22dB. * Use of \>2 topical (or any oral) IOP-lowering products at the baseline visit. * Any ocular pathology in either eye that may have interfered with the ability to obtain visual field, disc imaging, or accurate IOP readings such as uveitis, refractive opacification; * Eye drops such as neuroprotective therapies have been used in the past three weeks might affect this clinical study, for inclusion need 8 weeks of wash period. * Pregnant or nursing women; * Diabetes mellitus, definite impairment of liver and kidney function, or severe heart, liver or kidney diseases; * In the last three months, ophthalmic surgery (including cataract surgery) has been performed * Enrolled in other clinical study at the same time. * Could not complete the study according to the requirements in this research . * History of epilepsy or severe mental illness, including schizophrenia, bipolar disorder or severe depression